212 THE MINUTE ANATOMISTS 



he had previously observed in the oyster,^ the byssus by 

 which the mussel anchors itself, and the crystalline 

 style, which he supposed to be accessory to reproduction. 

 At last he found what he took to be the eggs adhering 

 in clusters to the outside of a mussel-shell. Each egg 

 occupied one of a number of cells which were arranged 

 in regular rows, and was furnished with sixteen long 

 filaments disposed in a circle. What he had really 

 found was a Polyzoan colony (Membranipora) ; his 

 embryos were the polyps, and the circle of filaments the 

 lophophore. 



He thought that the crystalline style of the mussel 

 was used to arrange the eggs (polyzoan polyps) on the 

 outside of the shell, and compared it to the ovipositor of 

 an insect, but in a postscript he assigns this function to 

 the foot. 



The naturalist's attention was next caught by what 

 he called pustules on the mussel-shells, which a glance 

 at his figure shows to have been acorn-barnacles. On 

 the top of the conical barnacle-shell he found an aperture 

 guarded by two valves, which opened when dipped in 

 sea-water, but closed and retracted when touched with 

 a needle. The eggs of the barnacle were discovered ; 

 other individuals which contained no eggs he naturally 

 but erroneously took to be males.^ 



In spite of his unlucky mistakes, Leeuwenhoek, as we 

 have seen, drew from his unsuccessful quest of mussel- 

 eggs two capital discoveries. Early investigators no 

 doubt labour under special difficulties, but they also 

 enjoy advantages of their own. 



^Phil. Trans., Feb. 1681-2. Heide (infra, p. 213) announced the same 

 discovery in 1683. 



2 A description of a stalked barnacle (Lepas), about as good as Leeuwenhoek's 

 acorn-barnacle (Balanus) was given a hundred years earlier by Pabius Columna 

 in his Piseivm aliquot plantarumque novarum historia. 4to. Neapoli. 1592. 



